Deforested areas may face severe drought in coming decades

The drying effects of deforestation in regions such as the Amazon have been mitigated by changes in global climate patterns, but in coming decades when rainfall patterns change back again, these areas could face severe drought, according to new research.

Despite the fact that deforestation in the Amazon Basin in South America is predicted to result in warming and drying of the land mass, between 1950 and 1990, there was a 20% increase in rainfall, which appears to be the result of worldwide shifts in rainfall patterns, say a team of scientists from Iowa State University (ISU). The team found that water vapour converging in tropical South America was an over-riding force in the climate of the region throughout this period.

“Many scientists have studied the effects of deforestation, but no one has paid much attention to interdecadal change (change over decades),” said Professor Tsing-Chang Chen, one of the lead researchers on the project. “That is a very important component missing from the studies. It needs to be considered to get a true reading of the effects of deforestation,” he said, adding that the millions of dollars worth of research projects into the effects of deforestation around the world may be resulting in erroneous conclusions.

“We believe that deforestation by itself will cause warming and drying of the Amazon region,” said Professor Eugene Takle, the second lead researcher. “But over the past 40 years, global circulation patterns have been pumping extra moisture into this region from the outside.”

“We expect in coming decades that this pattern may reverse,” Takle explained. “If and when that happens, then the deforestation drying that everyone expected will be made even worse by the drying due to the reversal of the global circulation. There may be drought never before experienced in this region. We likely will see effects much worse than those described by current deforestation-impact models.”

Chen points out that whilst the ISU research focused on the Amazon, other areas are experiencing large-scale deforestation, which should also be studied in the future. He added that a better understanding of global climate patterns would be helpful because what happens in South America might not hold for Africa, Southeast Asia or Malaysia.

A report into the study, Suppressing Impacts of the Amazonian Deforestation by Global Circulation Change, appears in the October issue of the Bulletin of the American Meteorological Society.

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